Anesthesia and analgesia
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Anesthesia and analgesia · Jan 1999
Clinical TrialCommon peroneal nerve stimulation for neuromuscular monitoring: evaluation in awake volunteers and anesthetized patients.
The study was conducted in two parts. First, evoked responses to common peroneal nerve stimulation at four electrode positions were tested in 25 awake volunteers. The initial threshold stimulus current (ITS) (minimal current producing dorsiflexion or eversion of the ankle joint and great toe) and the supramaximal stimulus current (SMS) (the point at which further increases in current did not produce increases in twitch tension) were defined. SMS was not reliably achieved using electrodes at each side of the fibular head. However, an exploratory electrode accurately located the nerve and enabled SMS in all volunteers (SMS/ITS = 3.4). Second, 16 anesthetized, paralyzed patients were studied. The common peroneal and ulnar nerves were stimulated simultaneously. Evoked tension was recorded at the adductor pollicis using a force transducer and at the great toe by a blinded observer. Reversal was given when the train-of-four count at the great toe reached four. Onset times were longer, and median posttetanic counts were greater, at the great toe compared with the adductor pollicis. Time from reversal to train-of-four ratio = 0.7 at the adductor pollicis was 207+/-160 s. We conclude that neuromuscular monitoring at the common peroneal nerve was not equivalent to monitoring at the ulnar nerve. ⋯ Accurate neuromuscular monitoring is important for patient safety. We studied the accuracy of monitoring at the common peroneal nerve in volunteers and patients. An exploratory electrode accurately located the common peroneal nerve. Monitoring at the common peroneal nerve was not equivalent to monitoring at the ulnar nerve in patients.
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Anesthesia and analgesia · Jan 1999
Clinical TrialA new approach for brachial plexus block under fluoroscopic guidance.
We performed the subclavian perivascular approach to the brachial plexus using contrast medium to confirm the location of the tip of the needle and the spread of the injected solution to obtain a high success rate and to minimize the risk of pneumothorax. Review of the cases led to the hypothesis that the solution injected inside the costal attachment of the middle scalene muscle spreads into the interscalene space. Because of the difference in the placement of the tip of the needle using our technique and the supraclavicular approach, including the subclavian perivascular approach, we termed our technique the supracostal approach. We conducted the present study to establish the supracostal approach by proving this hypothesis. A total of 173 blocks in 149 adult patients were studied. Eighty-four blocks in 74 patients were achieved by using the supracostal approach with contrast medium. The needle was inserted 1 cm lateral to the palpated subclavian artery and 1-2 cm above to the clavicle to touch a specific part of the first rib, which we believed to correspond to the inside of the costal attachment of the middle scalene muscle. After injecting the anesthetic solution with contrast medium, radiographs were obtained for each block, while computed tomographic (CT) studies were performed for five blocks. Five blocks in five patients were achieved by using the subclavian perivascular approach with contrast medium and both radiographs and CT studies. In addition, the anatomical difference between the two approaches was evaluated in five adult cadavers. Based on these studies, we determined the proper part of the first rib that corresponded to the inside of the costal attachment of the middle scalene muscle. Eighty-four blocks in the remaining 70 patients were performed with the supracostal approach without contrast medium. Of the 84 blocks with contrast medium, 80 (95%) produced successful blockade defined by sensory and motor examination. The radiological studies showed that, with the supracostal approach, the injected solution, which spread from the middle scalene muscle into the interscalene space, did not spread below the first rib. However, with the subclavian perivascular approach, the solution was confined within the perineural sheath and spread below the first rib to the axilla. The anatomical studies could explain this difference, revealing that the perineural space of the brachial plexus is not identical to the interscalene space. There was no failure in the 84 blocks performed with the supracostal approach without contrast medium after we determined the proper part of the first rib. We conclude that the supracostal approach to the brachial plexus is reliable, easy to perform, and associated with a low complication rate. ⋯ A new fluoroscopically guided approach for brachial plexus block has been established on the basis of anatomical and radiological studies to be reliable, easy to perform, and associated with a low complication rate.
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Anesthesia and analgesia · Jan 1999
Decrease in case duration required to complete an additional case during regularly scheduled hours in an operating room suite: a computer simulation study.
We used Monte-Carlo computer simulation to determine whether surgical or anesthetic interventions to achieve small decreases in case duration may create enough new open operating room (OR) time to permit an additional case to be scheduled for completion in an OR suite during regular working hours. We used rules for scheduling of cases assuming that OR personnel are compensated so that the OR suite can profit financially from decreasing case duration to complete an additional case during regularly scheduled hours. The decreases in each case's duration required to create enough new open OR time to reliably (> or =95%) schedule another case were 30-39 min, 79-110 min, and 105-206 min for OR suites with 1-15 ORs and mean case durations of 1, 2, or 3 h, respectively. ⋯ Computer simulation shows decreasing case duration is unlikely to create sufficient operating room time to reliably permit an additional case to be scheduled for completion during working hours. Additional cases may best be added to the operating room suite schedule by optimizing case scheduling, not by decreasing the duration of all cases in the suite.
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Anesthesia and analgesia · Jan 1999
Clinical TrialWithin-patient variability of myogenic motor-evoked potentials to multipulse transcranial electrical stimulation during two levels of partial neuromuscular blockade in aortic surgery.
Intraoperative recording of myogenic motor responses evoked by transcranial electrical stimulation (tcMEPs) is a method of assessing the integrity of the motor pathways during aortic surgery. To identify conditions for optimal spinal cord monitoring, we investigated the effects of manipulating the level of neuromuscular blockade (T1 response of the train-of-four (TOF) stimulation 5%-15% versus T1 response 45%-55% of baseline), as well as the number of transcranial pulses (two versus six stimuli) on the within-patient variability and amplitude of tcMEPs. Ten patients (30-76 yr) scheduled to undergo surgery on the thoracic and thoracoabdominal aorta were studied. After achieving a stable anesthetic state and before surgery, 10 tcMEPs were recorded from the right extensor digitorum communis muscle and the right tibialis anterior muscle in response to two-pulse and six-pulse transcranial electrical stimulation with an interstimulus interval of 2 ms during two levels of neuromuscular blockade. The right thenar eminence was used for recording the level of relaxation. The tcMEP amplitude using the six-pulse paradigm was larger (P < 0.01; leg and arm) compared with the amplitude evoked by two-pulse stimulation during both levels of relaxation. The within-patient variability, expressed as median coefficient of variation, was less when six-pulse stimulation was used. At a T1 response of 45%-55% of baseline, larger, less variable tcMEPs were recorded than at a T1 response of 5%-15%. Our results suggest that the best quality of tcMEP signals (tibialis anterior muscle) is obtained when the six-pulse paradigm is used with a stable level of muscle relaxation (the first twitch of the TOF-thenar eminence-at 45%-55% of baseline). ⋯ This study shows that six-pulse (rather than two-pulse) transcranial electrical stimulation during a stable anesthetic state and a stable neuromuscular blockade aimed at 45%-55% (rather than 5%-15%) of baseline provides reliable and recordable muscle responses sufficiently robust for spinal cord monitoring in aortic surgery.
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Anesthesia and analgesia · Jan 1999
The influence of surgical sites on early postoperative hypoxemia in adults undergoing elective surgery.
To determine the influence of the surgical sites on early postoperative hypoxemia, we studied postoperative hypoxemia in 994 patients, ASA physical status I or II, aged 18-68 yr, scheduled for various types of elective surgery. Patients were divided into three groups on the basis of the surgical sites: Group 1 = elective superficial plastic surgery (n = 288); Group 2 = upper abdominal surgery (n = 452); and Group 3 = thoracoabdominal surgery (n = 254). Anesthesia was maintained with 1%-2% enflurane and 67% nitrous oxide in oxygen; thiopental or fentanyl was given IV as required. SpO2 levels were recorded while patients breathed room air shortly after arrival in the recovery room (0 min) and 5, 10, 15, 20, 30, 40, 50, 60, 120, and 180 min thereafter. The results showed that during the early postoperative period, the degree of arterial desaturation and the incidences of hypoxemia (SpO2 86%-90%) and severe hypoxemia (SpO2 85%) were closely related to the operative sites and were greatest for thoracoabdominal operations, less for the upper abdominal operation, and least for the peripheral surgery. The incidence of hypoxemia and severe hypoxemia in the recovery room was 7% and 0.7%, respectively, in Group 1, 38% and 3% in Group 2, and 52% and 20% in Group 3. Mild airway obstruction and hypothermia in the postanesthesia recovery unit (PAR) were the predictive factors of early postoperative hypoxemia. We conclude that during the early postoperative period, there were significant differences in SpO2 levels and incidences of hypoxemia and severe hypoxemia among the three groups. ⋯ We found that the severity of arterial desaturation and the incidence of hypoxemia during the early postoperative period are closely related to the surgical sites and are strongest for thoracoabdominal surgery, less for upper abdominal surgery, and least for peripheral surgery.